Do you have any experience with either machines? Both are excellent. I don't know enough about the GS3's, but I do know the temp stability on the synesso's is insane... I've witnessed not even a tenth of a deg C change during a pour. Setup and maintenance of such machines is critical, get advice from site sponsors or industry folk.
It 'might' be the case that LM's are more easily serviced depending where in AU you are. I can't add much more to this thread due to lack of knowledge.
Aesthetically I prefer the look of the LM.
My dream machine is in fact a Linea, I'm a sucker for that clunky retro style